Various types of small particulate additives have been used in polymer compositions. For example, core-shell particles for use in plastic compositions as impact modifiers have been in use for many years. Rubber compositions may also include core-shell particles, as taught, for example, by U.S. Pat. No. 6,437,050. Living anionic polymerization methods are known for making core-shell nanoparticles. These may be formed by crosslinking polymer chains that are formed into a micelle. Furthermore, certain functionalized nanoparticles have also been synthesized.
As with any polymer composition, determining what functional groups on an additive will be useful with a particular polymer matrix is a challenge. In addition to the general unpredictability of the art, a particular challenge with functionalized polymeric nanoparticles is to maintain the stability of the particle suspension during the polymerization formation and to maintain while compounding with a polymer matrix. Furthermore, challenges are also present for efficient and thorough blending of the particles into a polymer system with uniform distribution.
Rubber polymeric matrices, in particular, may be advantageously modified by the addition of various nanoparticles. The physical properties of rubber moldability and tenacity can be improved through such additions. However, the simple indiscriminate addition of nanoparticles to rubber is likely to be inhomogeneous and cause degradation of the matrix material. Moreover, only the selection of nanoparticles having suitable size, material composition, and surface chemistry, etc., will improve the matrix characteristics. An efficient technique for blending the nanoparticles into the rubber to maximize uniform distribution is also desirable.